New characteristic of tensile stress–strain properties in rubbers

Abstract

Usually, the tensile stress–strain relationship in rubbers looks like an S-shaped curve. The knee point on a curve for non-crystallized gum is related to limited stretchability of the vulcanization network, hence it is observed for pure-gum and filler-loaded rubbers. The bending occurs when the rubber phase reaches a definite strain (start of developing limited network stretchability), so one may assume that at a knee point the strain in the rubber phase is the same for both pure-gum and filler-loaded rubbers. This assumption enabled normalization of stress–strain curves for pure-gum and filler-loaded rubbers and to use a single curve. Knee-point strain is not a geometrical phenomenon, but a structural characteristic of a rubber, since it is related to vulcanization network density, i.e. to the elastic modulus.